If you've managed to connect and then the daemon dies, it's most probably the ISP.
Some of them will kick you off if they're very busy, and you haven't been active for even a few seconds.
Might also be due to poor telephone-line quality.
Guess what -- As I was writing this, my pppd died!
--> Disconnecting at Tue Apr 26 23:31:30 2005
--> The PPP daemon has died: Lack of LCP echo responses (exit code = 15)
--> man pppd explains pppd error codes in more detail.
--> I guess that's it for now, exiting
--> Provider is overloaded(often the case) or line problem.
--> The PPP daemon has died. (exit code = 15)
This is rare for my ISP. But hey, it can happen to us all.
Note the bit about 'man pppd'...